Butt = yellow (acidic) = glucose fermented (should always happen)
Slant = yellow (acidic) = Sucrose and lactose ( if yellow one or the other fermented, or both)
Thiosulfate added as sulfur, media contains Fe. If thiosulfate is used sulfate is given off, it reacts with Fe, making FeS, black ppt.
Sulferate is only active at acidic pH, meaning carb had to be fermented.